Field of the Invention
The present embodiments relate to an image heating apparatus mounted on an image forming apparatus, such as an electrophotographic copying machine and an electrophotographic printer, and an image forming apparatus including the image heating apparatus.
Description of the Related Art
In an image forming apparatus, such as an electrophotographic copying machine and an electrophotographic printer, a fixing apparatus of a heat roller system is conventionally widely used as an image heating apparatus (fixing apparatus) configured to heat, pressurize and fix an unfixed toner image carried on a recording material to the recording material. In recent years, a fixing apparatus of a film heating system is also implemented from the viewpoint of quick start or energy saving.
The fixing apparatus of the film heating system is disclosed in Japanese Patent Application Laid-Open No. S63-313182 and Japanese Patent Application Laid-Open No. H04-44075. The fixing apparatus of the film heating system includes: a heater as a heating body; a fixing film as a flexible rotating body coming into contact with the heater to generate heat and rotate; and a pressure roller as a pressure member forming a fixing nip portion along with the heater through the fixing film.
The recording material carrying the unfixed toner image is introduced between the fixing film and the pressure roller at the fixing nip portion, and the recording material is sandwiched and conveyed along with the fixing film. In this way, the pressure at the fixing nip portion fixes the unfixed toner image to the recording material surface, while the heat of the heater is provided through the fixing film. Members with low heat capacity are used for the heater and the fixing film in the fixing apparatus. The heater as a heat source can be energized to generate heat at a predetermined fixing temperature only during the execution of image formation. Therefore, there are advantages that the waiting time from power-on of the image forming apparatus to an image formation executable state is short and that the power consumption during standby is significantly small.
In the system, the fixing film sandwiches and conveys the recording material while sliding relative to the heater. To stabilize the rotation of the fixing film in this case, a configuration of providing a heat-resistant grease as a lubricant between the fixing film and the heater is disclosed in Japanese Patent Application Laid-Open No. 2003-045615.
In recent years, an image forming apparatus and a fixing apparatus with a larger number of printed sheets (higher productivity) per unit time are highly demanded by users. To execute the heat fixing process in the image forming apparatus faster, the recording material needs to be conveyed at a higher speed, and the rotational speed (process speed) of the fixing apparatus needs to be increased.
However, the increase in the process speed increases the speed fluctuation from the rotational speed during the print operation to the stop of the rotation of the fixing apparatus after the end of the print operation. In this case, a large acceleration fluctuation occurs at the fixing nip portion, and unpleasant stick-slip sound may be generated at a timing of the stop of the rotation of the fixing apparatus depending on the situation. The stick-slip sound is often generated when the viscosity of the lubricant is lowered in a state in which the image heating apparatus is warmed up as the heat fixing process is repeated.